This invention relates to a device for the control and regulation of the upper feed mechanism in an overlock sewing machine.
The upper feed mechanism includes at least one upper feed dog which turns above a needle plate by utilizing in conjunction a vertical motion mechanism and a horizontal motion mechanism consisting of a control shaft which rotates on its axis, a slide lever which extends out from the control shaft, a slider attached to the slide lever, a support consisting of a sliding guide seat attached to a protruding section of the slider, and a drive attached to the slide which activates the upper feed dog to move in generally a horizontal fashion.
Obviously, an overlock sewing machine may be equipped, other than the lower feed dogs which work in conjunction with the needle plate, with an upper feed mechanism consisting of an upper feed dog which operates above a needle plate. In particular, the upper feed dog is activated to work in conjunction with one of the lower feed dogs in order to feed the fabric being sewn in the direction of the needle or needles during the sewing operation.
For this purpose, the upper feed dog moves basically in an elliptical motion, which is generated by means of a vertical motion mechanism which cooperates with a horizontal motion mechanism. These two mechanisms are synchronized and operate along a support shaft of the upper feed dog in order to make the upper feed dog oscillate in a vertical and in a horizontal fashion.
In summary, the horizontal motion mechanism allows for the use of many elements which work in conjunction in order to activate a shaft to turn around its axis. From this shaft extends an arm attached to the support shaft of the upper feed dog by means of pivot, in order to raise and lower the feed dog in the oscillating fashion indicated above.
The horizontal motion mechanism consists of a control shaft which oscillates around its axis, from which a slide lever extends. A slide is connected to the slide lever on one side at a movable projection attached to a guide seat connected to a support. On the other side, the slide consists of a pusher connected at a slot which is attached to a movable block guide which moves along a shaft. This movable block is rigidly attached to a fixed portion of the sewing machine and extends horizontally, perpendicular to the control shaft.
A connector extends from the block and moves across a slot in a fixed portion of the sewing machine and which extends parallel to the above-mentioned shaft. At the opposite end of the block, the connector is attached to turn at an end of the feed dog support shaft.
Operation of the horizontal motion mechanism allows the oscillating motion of the control shaft to be transmitted, by means of the slide lever and the slide, to the block which moves alternately in conjuntion with the shaft that supports it. The horizonal turning motion is thus transmitted to the upper feed dog shaft by means of the connector.
The horizontal motion mechanism also includes regulating devices which, acting on the support, move the slide along the slide lever and position said slide at the proper place along the slide lever. The position of the slide along the slide lever depends on the range of horizontal movement from the upper feed dog.
As described, the customary control devices raise various problems in operation in high speed machines.
The cause of these problems is primarily due to the fact that, in regard to the horizontal motion mechanism, the movement of the block along the shaft is obtained by force which, by means of the slide, is applied at points which are relatively far from the axis of the shaft on which the block is to slide. this results in flexing which is transmitted from the block to the shaft, and which is considerably increased by the effect of inertia which comes into play during operation. The presence of flexing causes strong friction between the block and the shaft which results in early and irregular wear of said elements and, in high speed machines, undesirable cut-offs.
These phenomena may be noted even if, in imperfect operation, the slot through which the connector is guided is not perfectly parallel to the shaft on which the block moves.
It is evident that precise operation is required and, although costly to manufacture, the slot and the shaft must be perfectly parallel. Notwithstanding the above, the parallel position of the slot and the shaft may be easily altered due to irregular wear of the shaft caused by the above-mention phenomena.
Another problem encountered in the devices described above is due to the fact that regulation of the horizontal motion of the upper feed dog causes an increase or decrease in said motion, either in moving toward the needle or needles when/they are inside the dog or in moving away from the needles(s). Regulation may be performed only within very restrictive limits, because too much of an increase in the motion may cause interference between the upper feed dog and the needle or needles.